The present invention relates to flowmeters and flow sensors of the no-moving-parts type utilizing a fluid oscillator so arranged that the frequency of oscillation is indicative of the flow rate being measured or indicated.
In flowmeters of the above type, a fluid amplifier is used which has fluid accelerating means for accelerating a jet of fluid into an interaction chamber where a portion of the jet is received by a pair of oppositely disposed fluid receivers in differentially variable amounts depending on the position of the jet. The position of the jet is controlled by opposing pressures exerted thereon laterally through control ports connected to the receivers through negative feedback conduits so that the jet oscillates. It is desirable that such flowmeters have a linear flow vs. frequency characteristic since the oscillation frequency is measured and used as an indication of the flow rate. Heretofore, such linearity has not been completely achieved and this has required external calibrating compensation either in the form of a calibrated bypass around the flowmeter or special compensation interposed in the flowmeter readout system. In the interest of improving accuracy and reducing cost, it is desirable to eliminate such external compensation schemes, particularly in extended range flowmeters operating over a wide range of flow conditions including laminar as well as turbulent flow. Such an extended range flowmeter is disclosed and claimed in a co-pending application of C. G. Ringwall, Ser. No. 738,067, filed Nov. 2, 1976 (Docket 267652EE1910A) which is assigned to the same assignee as the present invention.
Accordingly, it is an object of the invention to provide a flowmeter of the fluid oscillator type having an output characteristic that is essentially linear for a wide range of flow conditions so that external compensation for non-linearity is not required.
A further object of the invention is to provide a flowmeter of the fluid oscillator type having a novel construction of the fluid accelerating means providing a constant discharge coefficient for various flow conditions whereby a linear flow vs. frequency output characteristic of the flowmeter is obtained.
Another object of the invention is to provide a flowmeter of the fluid oscillator type that is insensitive to viscosity changes in the metered fluid.